The majority of modern engine designs utilise a double over-head camshaft (DOHC) configuration in which separate camshafts are used to activate the intake valves and the exhaust valves of the engine. Furthermore, it is well known that significant improvements in power output, fuel efficiency and emissions can be achieved by changing the timing of the valve events relative to the engine crankshaft, particularly if the timing of the intake and the exhaust valve events can each be varied independently of the other.
Control of the intake and exhaust valve timing is conventionally achieved by using a camshaft phasing system to drive each camshaft such that each camshaft may be rotated through a defined range of angles with respect to the drive from the crankshaft in response to control signals from the electronic engine control unit (ECU). Various different phasing systems are known from the prior art, but the majority of modern engines utilise vane-type phasers for this purpose.
EP 1 234 954 (U.S. Pat. No. 6,725,817), which is incorporated herein by reference, describes a double vane phaser that is able to control the timing of more than one set of cam lobes, and shows how such a device may be applied to a DOHC engine.
Vane type phasers use oil pressure signals from a hydraulic control valve to alter the valve timing in response to electrical signals from the ECU. A typical vane type phaser requires two oil feeds or supply lines, the first to advance the camshaft timing and the second to retard the camshaft timing. In order to control the intake and exhaust valve timing independently, a double vane phaser requires four oil feeds—a pair to control the intake timing and a pair to control the exhaust timing.
It has been proposed to engage these oil feeds into an open bore in the front of the phaser via an oil feed spigot mounted on the front cover of the engine. However, integrating the oil supply system into the front cover of the engine increases the overall length of the cylinder head and requires pressurised oil to be supplied to the front cover, which would not be the case in the majority of DOHC engines. Whilst there are many examples in the prior art of vane type phasers using control oil feeds that enter the phaser via the adjacent camshaft bearing, this would not be practical for a double vane phaser because of the space required for four separate oil feeds.
In most cases, the camshaft bearing adjacent the phaser is the most heavily loaded because it has to support the loads from the camshaft drive system as well as the loads from the valve train. This makes the adjacent bearing a particularly unattractive location for oil feeds, which significantly reduce the load carrying area of the bearing.